Use of oil shale ash in road construction: results of follow-up environmental monitoring.

Oil shale ash (OSA) was used for road construction in a pristine swamp area in East-Estonia during 2013-2014. OSA was used as a binder both in mass stabilization of soft peat soil and in the upper layer. Use of OSA in civil engineering always raises questions about the environmental safety of such activities. Post-construction environmental monitoring of the pilot section was carried out in 2014 and 2015. The monitoring program involved surface water and soil sampling campaigns. Samples were analyzed for selected constituents and parameters of environmental concern. The paper gives data for assessing the environmental impact and evaluation of potential risks associated with construction of roads using OSA. Leaching of hazardous compounds from the pilot section to surrounding aqueous environment was not observed during the monitoring program. Still, the road construction affected the concentration of sulfates in surrounding surface water. Also, the water-soluble content of barium in surface water correlated significantly with the concentrations of chloride and sulfate ion and electric conductivity of the surface water. Therefore, it is recommended to monitor the electric conductivity, concentrations of sulfates, chlorides, and barium in nearby surface water when OSA is used in road construction.